Rodrigo Duterte sits for the retreat session in the ongoing 28th and 29th ASEAN Summits at the National Convention Centre in Vientiane, Laos (AP)

Philippine president Rodrigo Duterte has met informally with President Barack Obama in a holding room before attending a gala dinner at a regional summit, officials said.

The brief meeting on Wednesday night took a little sting out of the soured relations caused by Mr Duterte's intemperate language in referring to Obama earlier this week. That caused Mr Obama to cancel a formal meeting scheduled for Tuesday.

Mr Yasay said: "I am happy. This shows that the relationship between the two allies is strong."

Mr Obama and Mr Duterte are in the Laotian capital along with other regional leaders for the summit.

Mr Yasay said: "They met at the holding room and they were the last persons to leave the holding room. I can't say how long they met. It all springs from the fact the relationship between the Philippines and the United States is firm, very strong. The basis for this relationship is historical and both leaders realise this. And I'm very happy that it happened."

On Monday, hours before arriving in Laos, Mr Duterte told Philippine reporters he would not accept questions from Mr Obama about extrajudicial killings that have occurred during his crackdown on suspected drug dealers and users.

More than 2,000 people have been killed in the crackdown since he took office on June 30.

"I do not have any master except the Filipino people, nobody but nobody. You must be respectful. Do not just throw questions. Putang ina, I will swear at you in that forum," Mr Duterte said, using the Tagalog phrase for "son of a bitch".

On Tuesday, Mr Duterte expressed regret over the remarks, but the damage was done.

A Philippine department of foreign affairs spokesman, Charles Joe, also said Mr Obama and Mr Duterte met in the holding room.

He said it was a mutually agreed meeting, but that he had no details of what was discussed.

Mr Obama and Mr Duterte entered the dinner venue separately, and were seated far apart and did not interact with each other during the dinner, which lasted an hour and 20 minutes.